28 For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical.
29 But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.
God told Abraham that he and his descendants would be blessed, God's chosen people. It is not being born as a Jew, but being reborn as a Jew that matters to God.